Abstract 18730: Activation of the Ubiquitin Proteasome System After Myocardial Infarction
The ubiquitin proteasome system (UPS) is the major pathway for protein degradation in the heart. Both activation and inhibition of the UPS have been described in heart failure and hypertrophy, but UPS function after myocardial infarction (MI) has not been investigated. The objective of this study was to explore proteasome function after MI and potential mechanisms for dysregulation.
Methods/Results: Mice were subjected to permanent ligation of the left coronary artery (MI) or sham surgery. By echocardiography, progressive left ventricular (LV) dilation and systolic dysfunction occurred over 8 weeks in MI vs. sham animals. 26S proteasome activity was analyzed at 2, 4, and 8 weeks after MI or sham surgery and comparisons were made with 2-way repeated measures ANOVA. ATP-dependent chymotrypsin-like activities were significantly increased 2 and 4 weeks after MI (2448 ± 104 [sham pooled, n=25], 3435 ± 285 FU [2 wk post MI, n=9], 3275 ± 193 [4 wk post MI, n=9], P<0.01 for both time points vs sham), but not 8 weeks after MI (3010 ± 90 FU, P>0.05 vs sham). UPS activation was confirmed by inducing MI in transgenic mice expressing a UPS surrogate substrate, GFPdgn. Protein expression of GFPdgn in border zones and remote areas was significantly decreased 2 weeks after MI (23 ± 11% and 33 ± 10% respectively vs sham, n=3/group, P<0.05), indicating accelerated degradation by the UPS. Comprehensive proteomic profiling of immunopurified cardiac 20S, 19S and 11S proteasomes was performed using mass spectroscopy (Orbitrap) and verified by western blotting for selected subunits. There were no significant differences in protein expression of any proteasome subunits, or in the content of phosphorylated 20S subunit alpha-7, in MI vs. sham animals. However, by MV151 labeling there was a significant increase in the availability of the active site of 20S subunit beta-1 in MI vs. sham animals (P=0.01).
Conclusions: The UPS is activated early following MI without changes in proteasome content but with enhanced access to the proteolytic core, suggesting a post-translational mechanism for increased substrate uptake. Further studies are needed to determine if proteasome activation is beneficial or detrimental to post-infarct remodeling and ventricular dysfunction.
- © 2010 by American Heart Association, Inc.